The present invention relates to a magnetic tape cassette, particularly to a magnetic tape cassette generally referred to as digital audio tape (DAT) cassette.
Recently, the size and weight of cassette tape recorders have been reduced, and magnetic tape cassettes for such recorders made compact. For such applications, audio magnetic tapes capable of recording and playback with good quality and at a high density and having a long recording/playing time have been strongly desired. A digital audio tape, for which an input signal is subjected to digital processing such as pulse code modulation prior to recording, is well known as a tape which meets the above requirement.
In a digital audio tape cassette, the range of recorded signal frequencies is about five times as wide as that of a conventional compact audio tape cassette. The digital audio tape cassette has a mechanism which enables the cassette to be used together with a rotary head. This mechanism includes a guard panel which closes over the front opening of the cassette and opens upward therefrom. The guard panel is provided to protect the tape from dust which, were it to enter the cassette and cling to the tape, would degrade the performance of the tape since the wavelength of the recorded signals on a digital audio tape is much shorter than for the conventional compact audio tape cassette.
Also, because the size of the digital audio tape cassette is much smaller than that of the conventional compact audio tape cassette, the digital audio tape cassette is likely to be carried outdoors more often than a conventional compact audio tape cassette. For this and other reasons, the digital audio tape cassette requires some means for preventing the tape from unwinding due to vibration of the cassette during transport. For this purpose, the digital audio tape cassette is provided with a hub brake to check the rotation of the hubs on which the tape is wound when the tape is not in use. The hub brake is urged toward the hubs by a spring so that sharp-edged lugs of the hub brake contact the hubs when the cassette is not in use. The lugs are moved out of contact with the hubs when the tape is to be recorded on or reproduced.
A digital audio tape cassette as discussed above is disclosed in Japanese Unexamined Published Utility Model Application No. 84787/88.
However, since such cassettes are small in size, it is not easy to assemble the components thereof. The hub brake is especially difficult to assemble due to the spring, and it often falls out of the cassette during assembly. Therefore, the assembly efficiency of the cassette is low.
Digital audio tape cassettes in which an engagement device is provided between the upper half portion of the casing body of the cassette and the hub brake to improve the ease of assembly of the cassette have been proposed in Japanese Unexamined Published Utility Model Applications Nos. 67374/87 and 69879/87 and Japanese Unexamined Published Patent Application No. 134874/87. However, such an engagement device, which is provided between the upper half portion of the casing body of the cassette and a flat portion of the hub brake, can readily contact the side edge of the wound magnetic tape, causing damage to the tape or placing an undesirable load on the tape. If such loading occurs, the tape cannot be run at the prescribed speed to properly perform recording and playback.
The present invention was achieved in order to solve the above-mentioned problems.
Accordingly, it is an object of the present device to provide a magnetic tape cassette having a hub brake for preventing the hubs of the cassette from moving which can be easily assembled and which does not interfere with the normal running of the tape.